1. Field of the Invention
The present invention pertains to the field of fasteners, and is especially applicable to fastening a pressure vessel to another object, especially another pressure vessel. The present invention pertains especially to means for fastening two rocket motors to one another, for example a booster rocket motor to a main rocket motor.
2. Background of the Invention and Material Information
The assembly and process of the present invention are especially related to the art of fastening rocket engines to one another. Multi-engine rocket-powered aircraft are well known. More than one rocket engine in a single aircraft (or spacecraft) can be utilized to extend the range and/or speed and/or payload of the craft. The addition of separate rockets can also be used to produce added directional control or special maneuverability, spin, etc., to the craft. Most commonly, one or more booster rocket engines are employed along side a main rocket engine, in order to increase the thrust.
U.S. Pat. No. 3,070,329 (HASBROUCK) relates to directional control for rockets. HASBROUCK utilizes a plurality of independent movable steering rockets which are fastened along side the main rocket engine, and which exert a steering thrust at an acute angle to the line of thrust of the main propulsive nozzle. The steering rockets are affixed to the main rocket with gimbal joints, as well as a supporting ring which is lugged. Two struts, comprising ball and socket joints on the respective ends thereof, are affixed to the steering rocket and the main rocket. The purpose of the steering rockets is to provide a means for steering the main rocket in the desired direction, and this is why the gimbal joint is utilized in fastening the steering rocket to the main rocket.
U.S. Pat. No. 3,532,304 (PYPTIUK) relates to rocket powered space vehicles in which four rocket motors ar equally spaced around the roll axis of the vehicle, universally mounted on a common frame. Each motor is separately mounted to a tubular thrust ring by means of a coupling. The coupling may be a ball and socket joint, and the coupling permits the motor to pivot relative to the thrust ring. The arms which connect the rocket nozzles to the non-pivoting portion of the machine may also be fitted with ball and socket joints.
U.S. Pat. Nos. 4,892,435, 4,904,109, and 4,909,659, all in the name of Robert ANDERSON, relate to interlocking structural members employing transverse locking wedges or locking means. ANDERSON fastens composite materials together. The composite materials comprise polymers having reinforcing fibers therein. All three of these patents are particularly directed at aircraft wing skins which are attached to a support substructure. The means of attachment is a fastenerless joint. Fastenerless joints are utilized in order to avoid the problem of leaks which are common when rivets are used to attach the aircraft wing skin to the supporting substructure. Fastenerless joints also avoid passing rivets through various plies of the laminated structure, a practice which can cause rupture of the wing skin. ANDERSON's fastenerless joint comprises a wedge which interlocks a wing skin structure to a support substructure. The wing skin laminate has hollowed projections for receiving mating recesses in the composite wing substructure. The wedge is forced into the hollow projections after the projections are interdigitated with the mating recesses in the composite wing substructure. The wedges are transversely positioned across the mating recesses, and extend therefrom axially, so that they serve to lock the wing skin structure to the supporting substructure.
It is important to utilize lightweight but structurally strong components in building rocket engines, in order to improve the thrust-to-weight ratio, and thereby to increase the payload capacity and/or the range and/or the speed of travel of the rocket. To this end, composite materials (i.e., fiber reinforced resins) have been developed and utilize extensively throughout the aeronautical industry.
Even the outer casing (i.e. housing or "skin") of the body of a craft can be made from such fiber reinforced composite materials. Some of these materials have a strength to weight ratio significantly higher than many of the metals traditionally used in the manufacture of aircraft body panels.
Still, it remains important to keep the craft as light as possible, to enhance the payload, range, and speed of the craft. Accordingly, such elements as the outer casing of a rocket engine are manufactured to as thin a gauge as possible, while simultaneously maintaining an adequate margin against structural failure, taking into account the various forces to which the casing will be subjected.
The outer casings of solid propellant rockets are typically manufactured thin enough that the internal pressure produced by the operation of the engine is high enough to cause the circumference of the casing to increase in size by about 1 percent. Such an increase can create tremendous shear forces at fixed points on the casing, for example, if the casing is fastened to another rocket engine with a rigid connection at a fixed location. Large shear forces either risk structural failure or require greater weight in order to achieve a level of structural strength to carry the force. Such shear forces can be especially troublesome if the casing is made of a fiber-reinforced polymeric resin, since the fibers are generally laid down in layers having a directional orientation and hence are much stronger in some directions than others. The layers having fibers oriented in the weakest orientation with respect to the direction of shear are subject to much increased risk of failure, which could cause a failure throughout the entire thickness of the casing.